FoxNews reports a former Marine — armed with a Glock 21 .45-caliber handgun with an illegal extended magazine — opened fire on a packed California country music bar Wednesday night, killing 12 people, including a veteran sheriff’s sergeant nearing retirement, officials said.

Authorities believe Ian David Long eventually turned the gun on himself, but not before the 28-year-old, dressed in all black, terrorized a crowd filled with college students at Borderline Bar & Grill in Thousand Oaks, Calif. Long’s body was found in an office near the entrance of the bar.

Sheriff Geoff Dean, who is set to retire on Friday, said Long may have suffered from post-traumatic stress disorder and was known to law enforcement officials due to several unspecified “contacts” stretching back multiple years. Long served in the Marine Corps from August 2008 to March 2013, with a deployment in Afghanistan between November 2010 and June 2011, military records show.

“We’ve had several contacts with Mr. Long over the years, minor events such as a traffic collision. He was a victim of a battery in a bar in 2015,” Dean said, adding that the bar in 2015 was a different establishment than Borderline.

Dean said the last interaction between Long and authorities occurred in April, when police officers were called to Long’s house in Newbury Park, about five miles from Borderline, after reports of a disturbance. When they arrived, officers found Long “irate and acting irrationally,” leading to a crisis intervention team being summoned. The team, however, cleared Long and said they didn’t feel he was qualified to be taken into custody.

“Obviously, he had something going on in his head that would cause him to do something like this. Obviously, he had some sort of issue,” Dean said of Long.

Photo Credit: (Ventura County Sheriff’s Office) Sgt. Ron Helus was among the 12 people killed

As for why he attacked the bar, “there’s no indication that he targeted the employees. We haven’t found any correlation,” the sheriff said. “Maybe there was a motive for this particular night, but we have no information leading to that at all.”

Long opened fire inside Borderline about 11:20 p.m., during the bar’s “college country night” event, authorities said. Dean said it appears Long shot the unarmed security guard first, turned to the right to shoot other security and staff members before opening fire on the rest of the patrons. No one at the venue was armed.

About 150 to 200 people, including students from California Lutheran University, private Christian school Pepperdine University and California State University Channel Islands, were inside Borderline when witnesses said Long tossed a smoke device into the crowd and then, amid the confusion, fired at least 30 shots.

Deputies and highway patrolmen arrived at the bar within minutes of receiving multiple 911 calls and began assessing the grim, gruesome situation, Sheriff Geoff Dean said during an earlier Thursday news conference.

“It is a horrific scene in there. There is blood everywhere,” Dean said. He later described it as “hell.”

Sheriff’s Sgt. Ron Helus, a veteran of 29 years, arrived first on the scene and immediately entered the bar with a patrolman after hearing gunfire. But as the two made their way inside, Helus was shot several times. The patrolman pulled…

Sgt. Ron Helus had been set to retire in the next year from the Ventura County Sheriff’s Office when, responding Wednesday to a call of a shooting, he entered the Borderline Bar & Grill. He died trying to stop the rampaging gunman, who killed 11 others in the attack. He’s a hero. pic.twitter.com/j5fxZjmCSg